1. Field of the Invention
This invention relates to lasers and, more particularly, to a laser construction which has at least two laser optical cavities complete with optical reflectors and means for supporting lasable media, on a single, mechanically integrated resonator structure.
2. Prior Art
In its basic aspects, a laser includes a lasable medium positioned between optical reflectors which resonantly reflect optical radiation emitted by the lasable medium back-and-forth through the lasable medium to produce stimulated emission of coherent optical radiation. The reflectors define a path therebetween for the resonant reflection, referred to in the art as the laser "optical axis"; and the reflectors, together with means for supporting the lasable medium along the optical axis, are referred to as the laser "optical cavity". Typically, one of the optical reflectors is partially transmissive and permits some of the coherent optical radiation to escape from the resonant optical cavity to thereby provide an output beam of coherent radiation.
It is important in achieving and maintaining appropriate lasing within the resonant optical cavity, that the reflectors be maintained in a predetermined and spaced-apart relationship with respect to each other, and that the position of the lasable medium relative to the optical axis be maintained. It should be appreciated that even slight changes in these relationships can result in serious output power losses, frequency changes, and the like. It has therefore become standard practice to provide a resonator structure which supports the mounts for the optical reflectors and the means for positioning the lasable medium. Such resonator structure is designed and fabricated to maintain the optical reflectors mounted thereto in a rigid positional relationship relative to each other and the lasable medium, despite variations in thermal conditions, limited vibrations, etc. Examples of resonator structures for ion gas lasers following particular designs are described in U.S. Pat. Nos. 3,864,029; 3,966,309; 4,143,339; and 4,201,951, all assigned to the assignee of the present invention, and the disclosures of which are hereby incorporated by reference. As described in those patents, the resonator structure design includes mounts for the optical reflectors and for the ion gas plasma tube maintained in a desired, predetermined relationship by a plurality (specifically three) metal alloy rods extending parallel to the optical axis of the laser and having a low coefficient of thermal expansion. One of these patents, No. 4,201,951, describes a gas ion laser having two separate plasma tube assemblies which are serially aligned with one another in one optical cavity, i.e., between a single set of optical reflectors.
Medical applications for lasers are numerous. Laser radiation is used in the detection and treatment of cancer. For example, a medical treatment utilizing a dye laser for the selective destruction of cancerous tissue is described on pages 130, 131 of an article in the May, 1982, issue of Life Magazine. A chemical called HPD is injected into a patient and selectively attaches to cancerous tissue. Red light from a dye laser is injected into the malignant tissue and strikes the HPD, which releases a form of oxygen which destroys the diseased cells. In other applications of dye lasers described in that magazine article, the red radiation from dye lasers is used to remove tumors of the mouth, larynx, bronchi, skin, and eyes. It should be readily apparent that these present uses and future uses of laser radiation will become more widespread as lasers become sufficiently reliable and simple to operate so that medical personnel can readily operate them in a clinical environment.
Many medical applications require radiation of a frequency which as a practical matter is only available from a dye laser. However, conventional dye lasers require a second laser for operation. That is, in order to make a dye lase, it must be irradiated with the output beam of a pump laser, such as a frequency-doubled YAG laser, an argon gas ion laser, or a copper vapor laser. Thus, two separate lasers must be provided for use of a dye laser. Because the beam of the pumping laser must be precisely directed to a location in the cavity of the dye laser in order to cause such dye laser to lase, a trained laser technician is almost mandatory before such a laser can be used. It will be appreciated that this has severely inhibited the use of the same in many environments, including medical environments. These problems are compounded when it is desired to increase the output of a dye laser by using more than one pump laser, with each precisely focused to a point in a dye laser stream.